Reproductive Biology in Wild and Silvicultural Managed Populations of Escontria chiotilla (Cactaceae) in the Tehuacán Valley, Central Mexico

Reproductive biology of the columnar cactus Escontria chiotilla was analysed in wild and silvicultural managed populations in the Tehuacán Valley, Central Mexico, where this cactus is under domestication because of its edible fruits. Anthesis is diurnal, flowers opening between 8:00 and 17:00 h, the period between 12:00 and 13:00 appearing to be crucial in pollination success since at this time the maximum opening of flowers, turgidity of stigma, and activity of flower visitors, as well as the highest nectar production and pollen release occur. The bees Apis mellifera, Bombus pensylvanicus and Xylocopa mexicanorum, and the hummingbirds Amazilia violiceps, Cynanthus sordidus and Cynanthus latirostris were the most frequent flower visitors during the crucial period, and were observed contacting both stamens and stigma of E. chiotilla. No differences were found in anthesis nor in flower visitors among both population types. Distances separating the populations studied and bridges of individuals of E. chiotilla between them are within the radius that bees and hummingbirds may travel, indicating that spatial barrier to pollen flow are unlikely. Breeding system is self-incompatible. Production of flowers occurs during the whole year in both population types, allowing continual pollen flow among them. This observation confirms reports of high gene flow among the populations studied in previous population genetics studies. The high pollen flow among wild and managed population explains that however the occurrence of artificial selection, the process of domestication is in incipient stages presumably because gene flow counteracts effects of artificial selection.